Patients who are shocked or dehydrated need fluid resuscitation. This may be with crystalloid, but if colloid is required, despite recent concerns regarding albumin, there is continuing support for its use in the paediatric population. Restoration of intravascular volume may re-establish urine output prior to the development of renal failure and a more prolonged period of oligo-anuria. Establishment of an adequate state of hydration removes the need for the kidneys to produce a concentrated urine, which is demanding of energy and oxygen. During this period of fluid resuscitation care must be taken to avoid fluid overload if ARF becomes established and urine does not flow. Once normal hydration is achieved, fluid balance is maintained by calculating fluid input equal to output (urine + other measurable losses) + insensible losses (300 - 400 ml/m2 per 24 hours). If urine output is insufficient to allow adequate fluid administration, dialysis is required.